1. Technical Field of the Invention
The present invention relates to a process for producing a sulfonylimide compound represented by the formula:
MN(SO2Rf1)(SO2Rf2) 
2. Description of Prior Art
Sulfonylimide compounds are safe as a solute of a battery electrolyte and battery electrolyte that uses the sulfonylimide compound as a solute has a high energy density and exhibits high conductivity. Hence, the sulfonylimide compounds are regarded as a promising solute of a battery electrolyte. Also, the sulfonylimide compounds are useful as a Lewis acid catalyst and an ionic conduction agent.
The sulfonylimide compounds represented by the formula (I) MN(SO2Rf1)(SO2Rf2) may be synthesized by the process proposed by D. D. Desmarteau et al. in INORGANIC CHEMISTORY VOL. 23, No. 23, P3720-3723 (1984).
In this synthetic method, as shown by the following formula, trifluoromethylsulfonyl fluoride is reacted with ammonium, the resulting product is treated using hydrochloric acid to produce trifluoromethylsulfonylamide, which is then reacted with sodium methylate and then with hexamethyldisilazane, and the resulting product is reacted with trifluoromethylsulfonyl fluoride, thus obtaining an imide sodium salt. 
However, this process involves multi-reaction steps and hence takes longer. Also, expensive hexamethyldisilazane must be used to obtain an intermediate, and the yield is as low as about 50%.
In the above-described formula (I), M represents any one of Li, Na, K and Cs among alkali metals of group Ia in the periodic table. Rf1 and Rf2, which may be the same or different, respectively represent any one of a straight chain or branched compound of a fluoroalkyl, perfluoroalkyl, fluoroallyl and fluoroalkenyl group having 1 to 12 carbon atoms (the same hereafter).
In the Japanese Patent Application National Publication No. Hei3-501860, a method is disclosed in which a silazane metal compound is reacted with a perfluorosulfonyl halide compound to obtain an imide compound. In the Japanese Patent Application National Publication No. Hei4-501118, a method is disclosed in which an ionic nitride is reacted with a halogenated sulfonic acid to obtain in imide compound.
However, the silazane metal compound and the ionic nitride used in each of the above prior art are expensive, and hence the above methods are not an economical production method.
Also, in the Japanese Patent Application Laid-Open(Kokai) No. Hei8-81436, a method is disclosed in which anhydrous ammonia or a sulfonylamide and a sulfonyl fluoride are reacted with a tertiary amine or a heterocyclic amine, and the reaction product is further reacted with, for instance, a hydroxide containing an alkali metal and an alkali earth metal to produce imide salts.
In this method, because the product in the first stage is generated as an amine salt, it must be further reacted with an inorganic salt. Also, since a tertiary amine or a heterocyclic amine is used in the reaction, problems concerning work environment caused by the odor and disposal of the amine occur. Moreover, because the anhydrous ammonia is always used, an autoclave as the reactor and a low temperature cooling unit are required. This method is, therefore, unsuitable for mass-production.
As outlined above, the prior art involves a long reaction step and uses expensive raw materials, and it is hence hard to say that these methods in prior art are industrially acceptable methods.
In the Japanese Patent Application Laid-Open (Kokai) No. Hei8-81436, anhydrous ammonia, a perfluoroalkylsulfonyl fluoride and a tertiary amine are reacted with each other. To obtain an imide salt, at least two steps are required; and in the reaction, a tertiary amine or a heterocyclic amine is used, causing possibility of pollution of work environment derived from the odor and the like. Further, the product must be reacted with an alkali metal or the like in an aqueous solution in the second step, and at this time, it is necessary to dispose the amine which is freed and distilled together with water, causing increased production costs.
It is an object of the present invention to solve these various problems and to produce a sulfonylimide compound industrially easily at a low cost in an efficient manner.
The inventors of the present application have made earnest studies to accomplish the above object and as a result found that a sulfonylimide compound (represented by the formula (I) MN(SO2Rf1) (SO2Rf2)) which is free from the foregoing problems can be produced industrially easily at a low cost in an efficient manner.
More specifically, the present invention comprises a reaction of at least one of the sulfonyl halogenides represented by the formula (II) RfSO2X with anhydrous ammonium or an ammonium salt in the presence of fluorine compounds represented by the formula (III) MF.
In the above-described formulas (I) and (II), M represents any one of Li, Na, K and Cs among alkali metals of group Ia in the periodic table, and X represents either F or Cl among halogen elements of VIIb group in the periodic table. Also, Rf in the above-described formula (II) represents the same or identical group as Rf1 or Rf2 in the formula (I).
The inventors have also found that sulfonylimide compound represented by the formula (I) MN(SO2Rf1) (SO2Rf2) can be produced in the mild conditions that anhydrous ammonium is not always used and in only one-step reaction by reacting a sulfonylamide represented by the formula (IV) RfSO2NH2, at least one of the sulfonyl halogenides represented by the formula (II) RfSO2X, and fluorine compound represented by the formula (III)MF with each other.
Li, Na, K, Rb, Cs and Fr exist as the alkali metals of Ia group in the periodic table. Among these metals, especially any one of Li, Na, K and Cs is selected and used. Therefore, in the case of these metals, the fluorine compounds that are used are LiF, NaF, KF (as KF, any one of calcine-dried KF (cd KF) and spray-dried KF (sd KF) produced by a spray drying method may be used) and CsF
The reason why Li, Na, K, and Cs are preferred among alkali metals of group Ia in the periodic table is that they are relatively cheap and suitable to produce sulfonylimide compounds industrially easily, at a low cost and in an efficient manner. Especially, K is prominent for the above property among Li, Na, K, and Cs.
In the present invention, on the other hand, the sulfonylimide compound can be produced by using an ammonium salt. As the ammonium salt in this case, it is desirable to use ammonium fluoride or ammonium hydrogendifluoride. These of either one of these compounds has the advantage that a specific reactor (autoclave) is not required.
CF3SO2Cl among sulfonyl halogenides represented by the formula (II) RfSO2X, which is sold on the market as a reagent, can be usually handled as liquid because its boiling point is 30xc2x0 C., relatively high among these kinds of compounds.
Although xe2x80x9csulfonylimidexe2x80x9d and xe2x80x9csulfonylamidexe2x80x9d in the present specification should be expressed formally as xe2x80x9csulfonimidexe2x80x9d and xe2x80x9csulfonamidexe2x80x9d, respectively, both are handled as the same significance.
The embodiment of the present invention will be hereinafter explained in detail.
The object compounds which has been produced in multi-steps in the prior art can be produced in one step by introducing a fluorine compound represented by the formula (III) MF, at least one of the sulfonyl halogenides represented by the formula (II) RfSO2X, and anhydrous ammonia or an ammonium salt into an inert solvent and reacting the mixture as shown by the following formula 2, 3, 4, and 5.
This is due to the basicity of the fluorine compound represented by the formula (III) MF.
(1) In the case where Rf1 and Rf2 in the formula (I) MN(SO2Rf1) (SO2Rf2) are the same or equal to each other: 
One mol of anhydrous ammonium, 2 mol of at least one of the sulfonyl halogenides represented by the formula (II) RfSO2X and 6 mol of a fluorine compound represented by the formula (III) MF are introduced into a reactor and the mixture is reacted in a solvent.
After completion of the reaction, 2 mol of the by-produced MX and 3 moles of hydrogendifluoride salt MFHF are removed by filtration, and the filtrate is concentrated. The sulfonylimide compound represented by the formula (I) MN(SO2Rf)2 can be thereby produced.
(2) In the case where Rf1 and Rf2 in the formula (I) MN(SO2Rf1)(SO2Rf2) are different from each other:
A sulfonylamide containing the Rf1 group which is produced by a known process shown below is reacted with at least one of the sulfonyl halogenides having a desired Rf2 group. A sulfonylimide compound with the Rf1 group and the Rf2 group are respectively constituted of an objective group can be thereby produced. 
(3) In the case of using an ammonium salt: 
wherein Rf1 and Rf2 are the same or different.
One mol of an ammonium salt, 2 mol of at least one of the sulfonyl halogenides represented by the formula (II) RfSO2X and 7 mol of a fluorine compound represented by the formula (III) MF are introduced into a reactor, and the mixture is reacted in a solvent.
After completion of the reaction, 2 mol of the by-produced MX and 4 mol of the by-produced hydrogendifluoride MFHF are removed by filtration, and then the filtrate is concentrated. The sulfonylimide compound represented by the formula (I) MN(SO2Rf1) (SO2Rf2) can be thereby produced.
These reactions can occur in a temperature range between about xe2x88x9230xc2x0 C. and 200xc2x0 C. At a temperature less than this range, the reaction rate is very low whereas at the temperature exceeding the above range, decomposition of the compounds, solvent and product to be used arises. A more preferable temperature range for the reactions is between 0xc2x0 C. and 100xc2x0 C.
As to the solvent, any solvent can be used without particular limitations as far as it is inert to the reaction materials. For example, ethers such as diethyl ether and tetrahydrofuran, halogenated hydrocarbons such as dichloromethane and dichloroethane, hydrocarbons such as benzene, heptane and hexane and nitrites such as acetonitrile can be used.
In order to produce various sulfonylimide compounds other than those described above, a sulfonylimide compound obtained by these production methods is made into an acid by using concentrated sulfuric acid and the acid is distilled to thereby synthesize a sulfonylimidic acid [HN(SO2Rf1)(SO2Rf2)]. This acid can be further reacted with a compound selected from hydroxides, oxides, carbonates and acetates of metals corresponding to this acid.
In this case, fluorine compounds represented by the formula (III) MF to be used in the synthesis of a sulfonylimide compound can be compounded and used.